If you live in or have visited the Southern Hemisphere, you may be familiar with the Magellanic Clouds. On a clear, dark night, the Large and Small Magellanic Clouds appear as two smudges of light in the southern sky. Stories have been told about these clouds throughout the ages and across cultures. For example, in the legends of indigenous Australians, these smudges are an elderly couple camping along a river; to the Sotho people of Southern Africa, they are tracks of celestial animals. Today, we know that these clouds are in fact nearby galaxies: they are members of the Local Group, the collection of galaxies to which our own Milky Way belongs. Both of the Magellanic Clouds have been intensively studied by astronomers, with the goal of understanding how other galaxies differ from our own.

Recently, a team of astronomers made an exciting new discovery: the Small Magellanic Cloud is actually two galaxies, not one. In their study, the scientists observed the movement of hydrogen gas within the Small Magellanic Cloud using ASKAP, a telescope located in Western Australia. They found that this motion was consistent with two different components: one moving with a speed of 170 km/s (about 400,000 miles per hour) and the other moving more slowly. Based on their results, the scientists concluded that the Small Magellanic Cloud is likely two galaxies, with one sitting behind the other from our point of view. The one in the back is 16,000 light years further away from us than the one in the front – roughly 1/12th of the total distance between us and the Small Magellanic Cloud(s).

Further work is required to determine whether these components are truly two independent galaxies, or if they were originally one galaxy that was split in two by interactions with the Large Magellanic Cloud. Despite the best efforts of astronomers, there is still much to learn about the features of our night sky that have captured humankind’s imagination for generations.

This study was led by Claire E. Murray, an assistant astronomer at the Space Telescope Science Institute in Baltimore, Maryland.

Managing Correspondent: Emily Pass

Press Article: Two SMCs are Better than One (Astrobites)

Original Journal Article: A Galactic Eclipse: The Small Magellanic Cloud is Forming Stars in Two, Superimposed Systems (arXiv preprint; accepted for publication in The Astrophysical Journal)

Image Credit: ESO/A. Santerne

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